1. Field of the Invention
This invention relates to rotary equipment and an oil pump. This invention can be utilized in an oil pump used in, for example, a power steering device of a vehicle.
2. Description of the Related Art
A related art of an oil pump is explained as a typical example of rotary equipment. There is a conventional oil pump that has a base part having a working chamber, suction port and discharge port, and a rotor provided rotatably in the working chamber of the base part (Japanese Patent Application Publication No. 2007-132237 (JP-A-2007-132237)). This rotor has a rotor main body and vanes fitted into grooves provided on an outer peripheral part of the rotor main body. The vanes move in a centrifugal direction and centripetal direction as the rotor rotates. Consequently, the pressure of a chamber between adjacent vanes fluctuates and thereby oil is suctioned from the suction port and discharged from the discharge port. Here, the base part is configured by a front housing and rear housing. The rear housing has an opposed sliding surface which faces a sliding surface of the rotor main body and a sliding surface of each vane. The rear housing is formed from aluminum-silicon based alloy to attain weight reduction, high wear resistance and high strength.
In recent years, the pressure of oil discharged from an oil pump has been increasing with the improved power of an internal combustion engine. Therefore, the opposed sliding surface of the housing such as the rear housing might be worn away progressively, depending on the operating condition of the oil pump.
Especially curvature deformation sometimes occurs on the rear housing, due to the increased pressure inside the oil pump. In this case, wear of the opposed sliding surface of the rear housing progresses easily. As a result, the oil might leak out from between the opposed sliding surface of the rear housing and the sliding surface of the rotor main body or between the opposed sliding surface of the rear housing and the sliding surface of the vane. Therefore, the oil pump may not be able to offer its own capability if used for a long period of time. In recent years, the sliding condition is becoming more severe in other rotary equipment as well, such as a compressor.
For this reason, in the oil pump disclosed in JP-A-2007-132237, the opposed sliding surface of the rear housing is provided with an anodized aluminum film obtained by anodization using a low-temperature sulfate bath, in order to improve the wear resistance. However, because the anodized aluminum film is formed from γ-alumina in the abovementioned anodization and the hardness of the anodized aluminum film is approximately Hv 230 to 450, the wear resistance is not sufficient.